Could the cover of the most profitable single-issue magazine franchise in the world be a barometer for the stock market? CNBC.com looked at the market performance in years when the magazine cover featured a blonde versus a brunette.

Additionally, the models' nationality may also yield an interesting result. Since 1978, the S&P 500 posted an average return of 14.3 percent when an American was on the cover of the magazine versus an 10.8 percent increase when a model from another country was selected, according to Bespoke Investment Group.

The following pages contain the Sports Illustrated covers associated with the best market years.